The present invention generally relates to power hand tools, and more particularly, to power reciprocating tools.
Reciprocating tools that are motor driven, such as saber saws, larger reciprocating saws and the like are usually driven by electric motors that have a rotating output shaft. The rotating motion is translated into reciprocating motion for moving a saw blade or the like in a reciprocating manner.
Reciprocating tools such as jigsaws, saber saws, as well as larger reciprocating saws are typically driven by the rotating output shaft of an electric motor. Such tools have a mechanism that translates rotary motion of the output shaft into reciprocating motion. With the recent emphasis on tool portability, drive motors are increasingly powered by rechargeable battery packs, and even relatively large reciprocating saws are now being powered by such battery packs. Because larger saws are often used for heavy duty jobs, it is important for the run time of the batteries between charges be sufficient that the user does not have to frequently change out and recharge the battery packs while working. Therefore, it is important that the design of such tools contributes to efficient operation.
Typical reciprocating saws have a plunge rod or plunger that is guided in its reciprocating movement by sliding in metal guide bushings. One of the bushings is nearly always located at the very front of the saw and is exposed to dust and debris during operation of the saw. The front bushing typically becomes loaded with dirt and also receives very little grease. Generally, poor lubrication combined with the high coefficiency of friction that sliding bushings typically have, results in considerable friction heating and power loss. Sliding plunge rod action in guide bushings typically wastes 50% or more of the power used in operation because of the sliding friction. If the design is one that has counterweights to reduce vibration, such counterweights are also often designed to slide in steel guide bushings. This therefore increases waste of energy and accordingly, most commercially available battery powered reciprocating saws at the present time simply do not have counterweights. This is undesirable because the absence of counterweights substantially increases the vibration that is experienced by a user during operation.
There has also been much research and development over the years in attempting to improve the cutting efficiency of such reciprocating saws and this has been achieved by introducing an orbital path of movement for the blade as it performs its cutting stroke as well as its return stroke. Such orbital as have the effect of increasing the force that is applied to the blade during its cutting operation. The amount of orbital action can often be varied by manipulation of a control mechanism associated with the tool, so that efficient cutting can be done. The adjustment of the amount of orbital action or variation of the cut path can be made to more efficiently cut both hard and soft materials. It is generally known that existing orbit systems work better in soft materials than they do in hard materials. For this reason, saws are provided with orbit on-off switches. Knowing when to turn the orbital action on or off and remembering to do so can lead to confusion by users.
Existing orbit mechanisms create a motion path that is related to the position of the plunger. The position of the plunger or plunger rod can be described as being fully forward, fully back or at mid-stroke in general. All existing orbit mechanisms cause the blade to start moving into the work piece at the start of a cut stroke and move away from or out of the work piece during the return stroke. The amount of incremental orbit motion in typical commercially marketed orbit systems is nearly constant during the entire cut stroke and the return stroke. The orbit path also can be said to be nearly symmetrical with respect to the cutting and return strokes.
These conventional orbit systems work well when cutting soft materials such as wood. However, when cutting hard materials such as steel, pipe or steel plate, conventional orbit systems have important drawbacks. Conventional orbit mechanisms apply orbital action at the start of a cut stroke. The orbital action often causes the blade to bounce on the material at the beginning of the cut stroke which delays good establishment of the blade teeth in the material for a portion of the cut stroke thereby reducing cutting effectiveness.
Mechanisms that can create substantial nonlinear orbit paths for aggressive orbit paths and end strokes with conventional orbit drive systems have often experienced significant mechanical limitations. These are typically cam systems that have linear motion which is basically symmetric about a mid-stroke position, with the cut stroke being one near linear path and the return stroke as another near linear path. These two paths are offset from each other by a small amount.
To date, no known attempts been made to create asymmetric or highly nonlinear paths. Attempts have been made to create a more aggressive orbit using cam drives. However, this results in very high cam follower loads which create high friction and wear in the cam elements. Another wear problem that occurs when the cam is aggressively shaped is that the cam follower can lift off of the cam. This produces a lack of contact between the cam and the cam follower for a major portion of the cam rotation. This is called cam float and is a common problem in high-speed cams. Floating results in loss of the force pushing the blade into the work piece. In especially aggressive cams, it can require several revolutions of the cam before the follower comes back down into contact with it. The loss of cam to cam follower contact then leads to the loss of contact force between the saw blade and the work piece and reduces the cutting rate instead of increases it.
There have been cam systems where the orbit actuation cycle of down and up is shared by two cams. However, having aggressively shaped cams is expensive because of the necessity of matching two cam profiles with a high degree of precision and the attendant wear problem still exists. Similar problems of high forces arising with aggressive orbits arise when trying to use adjustable angled slots with their associated slot followers. The forces that are experienced can be very high, even if the track is straight and too much orbital action will lead to high forces on the track follower. Since much of the action of a track follower involves sliding, high friction and wear are also a problem.